QR.Auxiliaries {base} | R Documentation |

## Reconstruct the Q, R, or X Matrices from a QR Object

### Description

Returns the original matrix from which the object was constructed or
the components of the decomposition.

### Usage

qr.X(qr, complete = FALSE, ncol =)
qr.Q(qr, complete = FALSE, Dvec =)
qr.R(qr, complete = FALSE)

### Arguments

`qr` |
object representing a QR decomposition. This will
typically have come from a previous call to `qr` or
`lsfit` . |

`complete` |
logical expression of length 1. Indicates whether an
arbitrary orthogonal completion of the **Q** or
**X** matrices is to be made, or whether the **R**
matrix is to be completed by binding zero-value rows beneath the
square upper triangle. |

`ncol` |
integer in the range `1:nrow(qr$qr)` . The number
of columns to be in the reconstructed **X**. The default
when `complete` is `FALSE` is the first
`min(ncol(X), nrow(X))` columns of the original **X**
from which the qr object was constructed. The default when
`complete` is `TRUE` is a square matrix with the original
**X** in the first `ncol(X)` columns and an arbitrary
orthogonal completion (unitary completion in the complex case) in
the remaining columns. |

`Dvec` |
vector (not matrix) of diagonal values. Each column of
the returned **Q** will be multiplied by the corresponding
diagonal value. Defaults to all `1` s. |

### Value

`qr.X`

returns **X**, the original matrix from
which the qr object was constructed, provided `ncol(X) <= nrow(X)`

.
If `complete`

is `TRUE`

or the argument `ncol`

is greater than
`ncol(X)`

, additional columns from an arbitrary orthogonal
(unitary) completion of `X`

are returned.

`qr.Q`

returns part or all of **Q**, the order-nrow(X)
orthogonal (unitary) transformation represented by `qr`

. If
`complete`

is `TRUE`

, **Q** has `nrow(X)`

columns.
If `complete`

is `FALSE`

, **Q** has `ncol(X)`

columns. When `Dvec`

is specified, each column of **Q** is
multiplied by the corresponding value in `Dvec`

.

`qr.R`

returns **R**. The number of rows of **R** is
`nrow(X)`

or `ncol(X)`

, depending on whether `complete`

is `TRUE`

or `FALSE`

.

### See Also

`qr`

,
`qr.qy`

.

### Examples

p <- ncol(x <- LifeCycleSavings[,-1]) # not the 'sr'
qrstr <- qr(x) # dim(x) == c(n,p)
qrstr $ rank # = 4 = p
Q <- qr.Q(qrstr) # dim(Q) == dim(x)
R <- qr.R(qrstr) # dim(R) == ncol(x)
X <- qr.X(qrstr) # X == x
range(X - as.matrix(x))# ~ < 6e-12
## X == Q %*% R if there has been no pivoting, as here.
Q %*% R

[Package

*base* version 2.5.0

Index]